This invention pertains to spectrophotometers and to methods of spectrophotometric analysis, and more particularly to spectrophotometers incorporating light omitting diodes as a source of radiation and methods in which such spectrophotometers are used.
Spectrophotometers are used to determine the amount of a substance contained in a solution. For example, a spectrophotometer may be used to determine the amount of hemoglobin contained in a blood sample. It is known that the concentration of a particular substance in a solution is related to the amount of light that the solution absorbs. Thus, the concentration of the substance can be determined by measuring the amount of light absorbed by the solution. This relationship between the amount of a substance in solution and the quantity of light absorbed is strictly obeyed only when substantially monochromatic radiation is used.
A typical spectrophotometer consists of a source of radiation such as an incandescent lamp, a wavelength control separate from the source of radiation, a container for the sample solution, a light receptor, and circuitry which converts the amount of light received at the receptor to an appropriate indication of the absorbance. The wavelength control in such a spectrophotometer is usually either a color filter or a monochromator, such as a prism or grating. This wavelength control is incorporated into the spectrophotometer so that the relationship between the concentration and the light absorption is strictly obeyed.
A substance may absorb different amounts of light at different wavelengths. For example, a solution of titanium formed with hydrogen peroxide has a peak absorbance of 0.90 at a wavelength of approximately 410 nanometers. At shorter and longer wavelengths, the absorbance drops significantly. When using spectrophotometric analysis, it is desirable to test a substance at its peak absorption wavelength because this will yield the most accurate results. Since different substances have peaks of absorption at different wavelengths, spectrophotometers have a number of color filters or other mechanisms for producing monochromatic light at various wavelengths.
One problem with spectrophotometers is that the wavelength control is complicated, expensive, and subject to errors. Where color filters are used for the wavelength control, a spectrophotometer must have many color filters as well as mechanisms to position these color filters. Where monochromators such as prisms or gratings are used, the positioning means for the prism or grating must be very accurate, since misalignment results in radiating the sample with a shorter or longer wavelength of light than intended, thus causing errors in determining the amount of sample present.